SMS Character Sets
Complete Guide to SMS Character Sets (GSM)
Overview
An SMS message can contain up to 160 characters when using the standard GSM (Global System for Mobile Communications) character set. When you use characters outside this set, your message automatically converts to Unicode format, which reduces the character limit to 70 characters and may result in higher messaging costs.
Character Encoding & Message Limits
Standard GSM Messages
- Single message: 160 characters
- Multi-part message segments: 153 characters each
- Uses 7-bit encoding
- Most cost-effective option
- Widely supported across all devices
Unicode Messages
- Single message: 70 characters
- Multi-part message segments: 67 characters each
- Uses 16-bit encoding
- Higher cost per message
- Required for non-GSM characters, emojis, and special symbols
Character Usage Guide
Common Problematic Characters
Below are frequently used characters that should be replaced with their GSM-compliant alternatives:
| Character to Avoid | GSM Alternative | Notes |
|---|---|---|
| ’ (curved quote) | ’ (straight quote) | Word processors often auto-convert these |
| ” (curved quotes) | ” (straight quotes) | Both opening and closing quotes need changing |
| – (en dash) | - (hyphen) | Common in copied web content |
| — (em dash) | - (hyphen) | Often used in formal writing |
| … (ellipsis) | … (three periods) | Counts as one character when using periods |
| • (bullet) | * (asterisk) | Common in formatted lists |
| ` (backtick) | ’ (straight quote) | Often used in technical writing |
| ” (smart quotes) | ” (straight quotes) | Auto-converted by word processors |
| ~ (tilde) | - (hyphen) | Common in technical content |
| ¬ (not sign) | - (hyphen) | Rare but problematic |
Standard GSM Character Set (7-bit)
Letters
- Uppercase: A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
- Lowercase: a b c d e f g h i j k l m n o p q r s t u v w x y z
Numbers
0 1 2 3 4 5 6 7 8 9
Basic Punctuation
. , ; : ? ! ” ’ ( ) / - _
Symbols
@ # % & * + = < >
Special Characters
- Greek Letters: Δ Φ Γ Λ Ω Π Ψ Σ Θ Ξ
- Accented Characters: é è ø ñ Ñ ü ä ö Ü Ö Å å É æ Æ ß Ç
- Space and Control: [space] [newline] [carriage return]
Extended GSM Characters (Counts as 2 Characters)
These characters are supported but each counts as two characters against your limit: [ ] ~ ^ € \ |
Best Practices for SMS Composition
Message Planning
- Draft your message in a plain text editor to avoid automatic character conversion
- Calculate character count before sending
- Include space for any personalization variables
- Consider message splitting points for longer content
Technical Considerations
- Test messages on multiple device types
- Use an SMS testing tool to verify character encoding
- Check character count using a GSM-specific calculator
- Verify support for special characters in target regions
Content Optimization
- Use abbreviated forms when appropriate
- Remove unnecessary punctuation
- Simplify formatting
- Use standard GSM characters whenever possible
Common Pitfalls to Avoid
Formatting Issues
- Copying from word processors without cleaning text
- Using rich text formatting
- Relying on special characters for emphasis
Technical Mistakes
- Assuming all special characters count the same
- Not accounting for message concatenation
- Ignoring character encoding in different regions
Content Problems
- Using emojis without understanding their impact
- Including URLs with special characters
- Not considering message splitting in natural break points
Impact on Message Costs
GSM Messages
- Standard rate applies
- More characters per message
- Better value for longer content
Unicode Messages
- Higher rate may apply
- Fewer characters per message
- May require more segments for same content
Cost Impact Analysis
Message Splitting Examples
-
Standard Message (GSM-7): Welcome to our store! Get 20% off your purchase today. Valid until December 31. (71 characters = 1 SMS)
-
Message with Special Characters (UCS-2): ✨ Welcome to our store! Get 20% off your purchase today! ⭐ (71 characters = 2 SMS)
Character Replacement Guide
| Special Character | GSM Alternative | Impact |
|---|---|---|
| ✨ (sparkle) | * (asterisk) | Saves 1 SMS |
| – (en dash) | - (hyphen) | Maintains GSM |
| ” (smart quote) | ” (straight quote) | Maintains GSM |
| • (bullet) | * (asterisk) | Maintains GSM |
| … (ellipsis) | … (periods) | Maintains GSM |
Best Practices for Cost-Effective SMS Marketing
Message Planning
- Draft in plain text first
- Calculate character count before adding special characters
- Consider message priority vs. cost
- Plan split points for longer messages
Marketing Considerations
- A/B Testing
- Test engagement with/without special characters
- Monitor ROI for decorated messages
- Track click-through rates
- Brand Voice
- Balance professionalism with personality
- Maintain consistency across campaigns
- Consider target audience preferences
- Strategic Use of Special Characters
- Use emojis to emphasize key points
- Place special characters at natural breaks
- Limit to one or two per message
Testing and Verification
Before Sending
- Use a GSM character checker tool
- Verify message length
- Test on multiple devices
- Check cost calculations
- Verify delivery format
After Sending
- Monitor delivery rates
- Check message appearance
- Track segmentation
- Analyze cost efficiency
- Gather recipient feedback
Conclusion
While special characters can enhance message engagement, their impact on costs requires careful consideration. Balance creativity with cost-effectiveness by using special characters strategically and monitoring their impact on campaign performance.